The word or phrase in a sentence or paragraph that a pronoun refers to is called its antecedent.

Muriel has become conscious of her appearance. She now thinks her eyes are too large. They have indeed become large and dark.

The antecedent of her and she is Muriel. The antecedent of they is eyes.

A pronoun and its antecedent must always agree in number – a singular noun has a singular pronoun and a plural noun has a plural pronoun.

Incorrect:

Jecko and Ezekiel treated his girl friends to lunch.

Jecko treated their girl friend to lunch.

Correct:

Jecko and Ezekiel treated their girl friends to lunch.

Jecko treated his girl friend to lunch.

A pronoun should also agree with its antecedent's gender.

Incorrect:

When Maria learned that he had gained two pounds in one week, he was greatly disappointed.

Correct:

When Maria learned that she had gained two pounds in one week, she was greatly disappointed.

In some sentences, the pronoun precedes its antecedent.

When she looked at Larry, Muriel blushed.

After she had reviewed her notes, Bettina felt more confident about passing the test.